A variety of antennas are used in radar, telecommunications, and other radio frequency (RF) systems. One common type of antenna is a dipole antenna, the most common of which is the half-wave dipole antenna. A half-wave dipole antenna is formed by two quarter-wavelength conductors, or elements, placed back-to-back for a total length of one-half wavelength. A standing wave on an element of one-half wavelength in length yields the greatest voltage differential, as one end of the element is at a node of the wave, and the other is at an antinode of the wave. The larger the voltage differential between the dipole elements, the greater the current between the dipole elements. The current is distributed along the length of the dipole, causing it to radiate an electric field (E-field) and a magnetic field (H-field). The direction of the E-field, represented by an E-field vector, is referred to as the polarization of the antenna.
Some RF systems utilize dual-polarization, or dual-polarized, antennas. For example, in the telecommunications industry, dual-polarization antennas are often found in base-station systems. A dual-polarized antenna can radiate in two directions within the E-field plane (E-plane), sometimes referred to as the polarization plane. In each direction, the generated E-field is polarized from the other and the two polarizations are typically orthogonal in the E-plane. Orthogonal polarizations ideally prevent power from one polarization from bleeding into another, which, when measured, is referred to as cross-polarization isolation or cross-polarization discrimination. However, polarizations can vary from perfectly orthogonal and therefore create power inefficiencies in the RF system caused by power transfer between polarizations.
Dual-polarized dipole antennas can be formed by arranging two linear-polarized antenna elements in a way that creates dual polarization. For example, a dual-polarized dipole antenna can be formed with one dipole antenna element rotated 90 degrees in the E-plane from another dipole antenna element. Each polarization need not be vertical or horizontal, in fact, it is common in the telecommunications industry to use plus-or-minus 45 degree, or slant, polarization, where the 45 degree offset of each polarization is with respect to the vertical or horizontal. In certain RF systems, the dual-polarized dipole antenna is duplicated to form an array that allows multiple simultaneous transmission and reception.